The plasterboards that are wasted amounts to about 1,500,000 tons a year, about 500,000 tons of which being chips and scraps stemming from the production and interior works of newly constructing the houses, and have been recycled by the plasterboard manufacturers. The rest of about 1,000,000 tons are those stemming from the remodeling and/or demolishing works of buildings such as houses, and have been buried in the reclaiming sites. However, the amounts of the waste plasterboards are on the increase year after year, and it has been urged to effectively reuse the waste plasterboards from the standpoint of the shortage of reclaiming sites and load on the environment.
The plasterboard has, usually, been used in the form of a laminate with the paper by bonding a board paper onto the surface of the plaster substrate. The board paper is bonded to the plaster substrate by directly sticking the board paper onto the surface of the paste-like plaster blended with a water-soluble adhesive such as starch.
To effectively recycle the waste plaster, therefore, the plaster substrate and the paper must, first, be separated away from each other. A mixture of the plaster and the paper at present finds no use and is, therefore, buried in the administered reclaiming sites. Therefore, many methods have been proposed for separating the mixture into the plaster and the paper so that both of them can be effectively utilized again.
The methods can be roughly divided into those for stripping the paper off the plaster substrate without using liquid medium such as water (hereinafter called dry methods) and those for stripping the paper off the plaster substrate by using a liquid medium such as water (hereinafter called wet methods).
As the dry methods, patent document 1 proposes a method of separating the plaster and the paper from each other by pulverizing the waste plasterboard, roughly stripping the paper off the plasterboard (plaster substrate), recovering the papers of relatively large sizes through a sieve of a predetermined mesh size, and blowing the air at a predetermined flow rate to the papers of small sizes. Patent document 2 proposes a method of separating the plaster and the paper from each other by pulverizing the brittle plaster substrate by passing the waste plasterboard through a roller type-breaker having protrusions on the circumferential surface of the roll. Patent document 3 proposes a method wherein the waste plasterboard is pulverized to roughly separate the paper and the plaster from each other, and the plaster adhered to the paper is stripped off by using rollers having protrusions.
As the wet methods, patent document 4 proposes a method of heating the waste plasterboard and, thereafter, separating the paper from the plaster by feeding water thereto, and patent document 5 proposes a method of separating the plaster and the paper from each other by wet-heat-treating the waste plasterboard under the application of a pressure.                Patent document 1: JP-A-10-286553        Patent document 2: JP-A-2000-254531        Patent document 3: JP-A-2004-122076        Patent document 4: JP-A-6-142638        Patent document 5: JP-A-2004-307321        